That’ll be tough but I think it can be done on that tight budget. Doing something on commission is going to cost you but you may be able to find someone to do the outfit. The thing is the top and pants have to match, so it can't really be bought. Even simple costumes can run anywhere from $75-$500 or more. Sadly, I've been searching for some cheap ones for a while and it just isn't easy to find a pre-made costume for cheap.
For the accessories the key is to search out sales, thrift stores and start by making them by hand.
The belt reminds me of a seatbelt belt, this picture isn’t exact but its close. I think you could make alterations to it.
http://www.etsy.com/...nap-style-wreal
Or you could try a simple belt buckle like this
http://www.mensbeltb...a9524f54af6.jpg
The necklace will be a piece of cake. Any craft store will sell a cross like that in the jewelery making section. You may want to think of saving money by doing the detail work yourself and just having someone sew the basic pattern.